Pour the olive oil into a frying pan over medium/high heat. Once the oil is hot, add in the diced onions and mix to coat. Add in the pressed garlic cloves and mix; lower to medium heat.
While the onions and garlic are cooking, peel and dice the eggplant; add to the frying pan with the onions and mix. Peel and dice the zucchini; add to the frying pan and mix. Dice the tomatoes; add to the frying pan and mix. Season with a dash of salt.
Allow all the veggies to cook together for about 15-20 over medium/high heat with the cover on. Stir occasionally to prevent sticking. Once you see that the veggies have cooked through, lower the heat and let them simmer for another 15-20 minutes or until you're ready to serve.